EP3387024B1 - Monofunctional or telechelic copolymer of 1,3-diene and ethylene or alpha-monoolefin - Google Patents

Description

The present invention relates to copolymers of conjugated diene and monoolefin, which copolymer bears at least one functional group, as well as their method of preparation.

It is always of interest to have new polymers available in order to broaden the range of materials already available and improve the functionalities of already existing materials. Generally, the development of new polymers is motivated to improve the performance of already existing materials.

Among the access routes to new polymers, mention may be made of the modification of already known polymers. The modification of already known polymers can consist of a post-polymerization modification, modification which takes place on the polymer synthesized beforehand, such as for example the hydrogenation reaction or the grafting of function along the polymer chain, in the copolymerization of a functional monomer, in the use of a functionalizing agent in the polymer chain termination reaction or in the polymer chain initiation reaction.

The Applicants have already developed the synthesis of copolymers of conjugated diene and monoolefin, described for example in the patent applications EP 1092 731 , WO 2004035639 , WO2005028526 , WO 2007054223 And WO 2007054224 . In its efforts to modify the properties of these copolymers, the Applicants have discovered a new process which makes it possible to provide at least one function to these copolymers and thus to gain access to the synthesis of new copolymers. This process which uses a functional transfer agent not only allows the synthesis of copolymer of conjugated diene and monoolefin, which copolymer bears a function on one end of the copolymer chain, but also opens the way to the synthesis of copolymers of conjugated diene and telechelic or hetero-telechelic monoolefin.

• la chaîne copolymère A étant une chaîne copolymère comprenant des unités monomères M1 et des unités monomères M2, M1 étant un diène conjugué,
• B1 étant choisie dans le groupe constitué par N(SiMe₃)₂ ; N(SiMe₂CH₂CH₂SiMe₂) ; para-C₆H₄(NMe₂); para-C₆H₄(OMe) ; para-C₆H₄(N(SiMe₃)₂) ; ortho-CH₂-C₆H₄NMe₂ ; ortho-CH₂-C₆H₄OMe ; C₆F₅ ; C₃F₇ ; C₆F₁₃ ; CH(OCH₂CH₂O) ;
• B2 étant une fonction dérivant de B1.
• la fonction B étant portée en extrémité de la chaîne copolymère A,
• M2 étant l'éthylène ou un mélange d'éthylène et d'une α-monooléfine.

Thus, a first object of the invention is a copolymer comprising a copolymer chain A bearing a function B chosen from the group consisting of the functions B1 and B2,

• the copolymer chain A being a copolymer chain comprising monomer units M1 and monomer units M2, M1 being a conjugated diene,
• B1 being chosen from the group consisting of N(SiMe ₃ ) ₂ ; N(SiMe ₂ CH ₂ CH ₂ SiMe ₂ ); para-C ₆ H ₄ (NMe ₂ ); para-C ₆ H ₄ (OMe); para-C ₆ H ₄ (N(SiMe ₃ ) ₂ ); ortho-CH ₂ -C ₆ H ₄ NMe ₂ ; ortho-CH ₂ -C ₆ H ₄ OMe; _{C6F5 ; C3F7 ; C6F13 ;} CH(OCH ₂ CH ₂ O);
• B2 being a function deriving from B1.
• the function B being carried at the end of the copolymer chain A,
• M2 being ethylene or a mixture of ethylene and an α-monoolefin.

Another object of the invention is a process for preparing the copolymer in accordance with the invention.

• ∘ y étant égal à 2 ou 3,
• ∘ lorsque y = 2, le symbole Y étant un alcalino-terreux ou le zinc, et lorsque y = 3, Y étant l'aluminium ;
• ∘ d étant un nombre entier de 0 à 50, avantageusement de 0 à 11 ;
• ∘ B1 étant choisi dans le groupe constitué par N(SiMe₃)₂; N(SiMe₂CH₂CH₂SiMe₂); para-C₆H₄(NMe₂); para-C₆H₄(OMe); para-C₆H₄(N(SiMe₃)₂); ortho-CH₂-C₆H₄NMe₂; ortho-CH₂-C₆H₄OMe; C₆F₅; C₃F₇; C₆F₁₃; CH(OCH₂CH₂O).

An object described herein is the use of a transfer agent of formula (III) in the synthesis of copolymer in accordance with the invention,

Y((CH ₂ ) _d B1) _y (III)

• ∘ y being equal to 2 or 3,
• ∘ when y = 2, the symbol Y being an alkaline earth metal or zinc, and when y = 3, Y being aluminum;
• ∘ d being an integer from 0 to 50, advantageously from 0 to 11;
• ∘ B1 being chosen from the group consisting of N(SiMe ₃ ) ₂ ; N(SiMe ₂ CH ₂ CH ₂ SiMe ₂ ); para-C ₆ H ₄ (NMe ₂ ); para-C ₆ H ₄ (OMe); para-C ₆ H ₄ (N(SiMe ₃ ) ₂ ); ortho-CH ₂ -C ₆ H ₄ NMe ₂ ; ortho-CH ₂ -C ₆ H ₄ OMe; _{C6F5 ; C3F7 ; C6F13 ;} CH(OCH ₂ CH ₂ O).

The invention also relates to a compound of formula (II), intermediate compound in the synthesis of the copolymer in accordance with the invention,

Y(A-(CH ₂ ) _d -B1) _y (II)

in which Y, d, y, A and B1 are as previously defined.

The invention also relates to a rubber composition comprising the copolymer in accordance with the invention.

1. DETAILED DESCRIPTION OF THE INVENTION

Any interval of values denoted by the expression "between a and b" represents the range of values greater than "a" and less than "b" (that is to say limits a and b excluded) while any interval of values denoted by the expression "from a to b" means the range of values going from "a" to "b" (that is to say including the strict limits a and b).

By the expression "based on" composition, it is meant in the present description a composition comprising the mixture and/or the in situ reaction product of the various constituents used, some of these basic constituents (for example the elastomer, the filler or other additive conventionally used in a rubber composition intended for the manufacture of tires) being capable of, or intended to react with each other, at least in part, during the various phases of manufacture of the composition intended for the manufacture of tires.

The copolymer in accordance with the invention has the essential characteristic of comprising a copolymer chain A. The copolymer chain A comprises monomer units M1 and monomer units M2, M1 being a conjugated diene and M2 being ethylene or a mixture of ethylene and an α-monoolefin. By definition, the respective molar percentage of monomer units M1 and monomer units M2 in the copolymer chain A is strictly greater than 0.

The monomer units M1 result from the insertion of the monomer M1, a conjugated diene, in the growing copolymer chain A, in particular by a 1,2 or 1,4 addition. By “a” conjugated diene is meant one or more conjugated dienes. In the case where M1 represents a mixture of conjugated dienes, the monomer units M1 designate the monomer units resulting from the insertion of each of the conjugated dienes.

The M2 monomer units result from the insertion of the M2 monomer into the growing copolymer A chain. The term “an” α-monoolefin is understood to mean one or more α-monoolefins. In the case where M2 represents a monomer mixture, that is to say a mixture of several monomers, the monomer units M2 designate the monomer units resulting from the insertion of each of the monomers of the monomer mixture.

By way of conjugated diene, mention may be made of 1,3-dienes, particularly a conjugated diene chosen from the group consisting of 1,3-butadiene, isoprene and their mixture. Preferably M1 is 1,3-butadiene.

As α-monoolefin, suitable are aliphatic or aromatic α-monoolefins, particularly aliphatic α-monoolefins preferably having 3 to 18 carbon atoms such as propene, 1-butene, 1-hexene, 1-octene, 1-hexadecene or mixtures thereof.

According to one embodiment of the invention, the monomer units M1 represent more than 40%, preferably more than 60% by mole of the monomer units of the copolymer.

According to another embodiment of the invention, the monomer units M1 represent less than 35% by mole of the monomer units of the copolymer.

According to a particular embodiment of the invention, the ethylene units represent more than 50%, preferably more than 65% by mole of the monomer units of the copolymer.

According to a preferred embodiment of the invention, the monomer units M1 contain more than 80% by mole of unit resulting from a 1,4-trans insertion of M1 in the copolymer chain.

According to any one of the embodiments of the invention, the copolymer preferably contains less than 0.5% by mole of aliphatic hydrocarbon-based cyclic units, more preferably is devoid of such units, the cyclic unit containing a cycle with 5 or 6 carbon atoms.

According to an advantageous embodiment of the invention, the copolymer in accordance with the invention is a copolymer of M1 and of M2, in particular a copolymer of 1,3-butadiene and ethylene or a terpolymer of 1,3-butadiene, ethylene and an α-monoolefin as defined above.

According to any one of the embodiments of the invention, the copolymer preferably has a number-average molar mass (Mn) of at least 5000 g/mol, more preferably of at least 60,000 g/mol, a particularly advantageous minimum value for use of the copolymer as an elastomer, for example in a rubber composition for tires. Generally, its number-average molar mass does not exceed 1,500,000 g/mol; beyond this value the viscosity of the copolymer can make the use of the copolymer tricky. It preferably has a polydispersity index λ equal to Mw/Mn (Mw being the weight-average molar mass) of between 1.20 and 3.00. The values of Mn, Mw and Ð are measured according to the method described in paragraph II.1.

The copolymer chain A has the other essential characteristic of carrying a function B at the end. The function B can be attached to the copolymer chain directly by a covalent bond or via a divalent group of formula (I)

-(CH ₂ ) _w - (I)

in which w is an integer from 1 to 50, preferably from 1 to 11. Advantageously w is equal to 3.

Function B is chosen from the group consisting of functions B1 and B2. B1 is selected from the group consisting of N(SiMe ₃ ) ₂ ; N(SiMe ₂ CH ₂ CH ₂ SiMe ₂ ); para-C ₆ H ₄ (NMe ₂ ); para-C ₆ H ₄ (OMe); para-C ₆ H ₄ (N(SiMe ₃ ) ₂ ); ortho-CH ₂ -C ₆ H ₄ NMe ₂ ; ortho-CH ₂ -C ₆ H ₄ OMe; _{C6F5 ; C3F7 ; C6F13 ;} CH(OCH ₂ CH ₂ O). B2 is a function deriving from B1.

By function deriving from B1 is meant a function which is obtained by modification of the function B1 according to the reactions known to those skilled in the art.

Function B1 is advantageously the N(SiMe ₂ CH ₂ CH ₂ SiMe ₂ ) group or the N(SiMe ₃ ) ₂ group. Function B2 is advantageously chosen from the group consisting of amines, ammoniums and ketones. When B2 is an amine, it is typically obtained by deprotection of the N(SiMe ₂ CH ₂ CH ₂ SiMe ₂ ) group or of the N(SiMe ₃ ) ₂ group, optionally followed by an alkylation, according to reactions well known to those skilled in the art. When B2 is an ammonium, it can be obtained by modification of the same N(SiMe ₂ CH ₂ CH ₂ SiMe ₂ ) or N(SiMe ₃ ) ₂ groups, for example by quaternization reaction according to methods well known to those skilled in the art. When B2 is a ketone, it is advantageously obtained by deprotection of the acetal function CH(OCH ₂ CH ₂ O), a process also well known to those skilled in the art.

According to a preferred embodiment of the invention, B2 is a primary, secondary or tertiary amine, preferably a primary amine.

According to a particular embodiment of the invention, function B is function B1.

According to a variant of the invention, the copolymer carries a second function, Z function. The Z function is preferably carried on one chain end of the copolymer A. When the copolymer carries a B function and a Z function both at the end of the chain, the two functions are carried respectively by different ends: the copolymer is said to be telechelic or heterotelechelic in the particular case where Z is different from B.

According to any one of the embodiments of this variant, the function Z is preferably chosen from halogens, groups comprising an unsaturated carbon-carbon bond and functions containing a heteroatom chosen from S, N, Si, O, B and P.

According to any one of the embodiments of the invention, the copolymer is preferably linear.

The copolymer in accordance with the invention can be prepared by the process described below.

• (a) la préparation d'un composé de formule (II)
  
          Y(A-(CH₂)_d-B1)_y     (II)
  
  dans laquelle
  • ∘ y est égal à 2 ou 3,
  • ∘ lorsque y = 2, le symbole Y est un alcalino-terreux ou le zinc, et lorsque y = 3, Y est l'aluminium ;
  • ∘ d est un nombre entier de 0 à 50, avantageusement de 0 à 11;
  • ∘ le symbole A représentant la chaîne copolymère A décrite précédemment ;
  • ∘ B1 est choisi dans le groupe constitué par N(SiMe₃)₂; N(SiMe₂CH₂CH₂SiMe₂); para-C₆H₄(NMe₂); para-C₆H₄(OMe); para-C₆H₄(N(SiMe₃)₂); ortho-CH₂-C₆H₄NMe₂; ortho-CH₂-C₆H₄OMe; C₆F₅; C₃F₇; C₆F₁₃; CH(OCH₂CH₂O)
• (b) une réaction de terminaison de la chaîne copolymère A,
• (c) une réaction de modification de la fonction B1, notamment pour former la fonction B2.

The process for preparing the copolymer has the essential characteristic of comprising the following steps (a) and (b), and if necessary the following step (c):

• (a) the preparation of a compound of formula (II)
  
  Y(A-(CH ₂ ) _d -B1) _y (II)
  
  in which
  • ∘ y is equal to 2 or 3,
  • ∘ when y = 2, the symbol Y is alkaline earth or zinc, and when y = 3, Y is aluminum;
  • ∘ d is an integer from 0 to 50, advantageously from 0 to 11;
  • ∘ the symbol A representing the copolymer chain A described above;
  • ∘ B1 is chosen from the group consisting of N(SiMe ₃ ) ₂ ; N(SiMe ₂ CH ₂ CH ₂ SiMe ₂ ); para-C ₆ H ₄ (NMe ₂ ); para-C ₆ H ₄ (OMe); para-C ₆ H ₄ (N(SiMe ₃ ) ₂ ); ortho-CH ₂ -C ₆ H ₄ NMe ₂ ; ortho-CH ₂ -C ₆ H ₄ OMe; _{C6F5 ; C3F7 ; C6F13 ;} CH(OCH ₂ CH ₂ O)
• (b) a copolymer A chain termination reaction,
• (c) a modification reaction of function B1, in particular to form function B2.

According to a variant of the process, step (b) is a reaction of the compound of formula (II) with a compound comprising an acid proton, called a stopper (or stopper). As a stopper, mention may be made of water, carboxylic acids, in particular C ₂ -C ₁₈ fatty acids such as acetic acid, stearic acid, aliphatic or aromatic alcohols, such as methanol, ethanol, isopropanol, phenolic antioxidants, primary or secondary amines such as antioxidants comprising the diaminophenylene unit. This variant of the process makes it possible to synthesize a copolymer comprising a monofunctional copolymer chain, since the copolymer chain A of the copolymer bears the function B1 at the end of the chain provided by step (a) of the process.

According to another variant of the invention, step (b) is a reaction of the compound of formula (II) with a functionalizing agent. The functionalization reaction involves the breaking of the bond formed by Y and the carbon both adjacent to Y and belonging to the copolymer chain A. The functionalization agent is chosen by the person skilled in the art for its reactivity vis-à-vis this bond and for the chemical nature of the Z function that it carries. Step (b) then being a functionalization reaction, the method allows access according to this other variant to a telechelic or hetero-telechelic copolymer, since one end of the copolymer chain A carries the B1 function provided by step (a), and the other end the Z function provided by step (b).

Generally, the termination reaction is carried out by bringing the polymerization reaction medium into contact with a termination agent, whether it is a stopper or a functionalizing agent, at a monomer conversion rate chosen by the person skilled in the art according to the desired macrostructure of the copolymer.

Step (c) is an optional step depending on whether or not it is desired to transform function B1, in particular into function B2. The embodiment of the method which comprises step (c) can be applied to the two variants of the method described previously. In certain very particular embodiments, step (c) can be carried out simultaneously with step (b). By way of example where step (b) and (c) are concomitant, mention may be made of the case where step (b) is a termination reaction with an acid compound and step (c) is a deprotection reaction of the B1 function under acidic conditions.

According to a particular embodiment of the invention, step (c) is a reaction for deprotection of the function B1 in B2, carried out in an acidic or basic medium depending on the chemical nature of the function B1 to be deprotected. For example, the trimethylsilyl group which protects the amine function can be hydrolyzed in an acidic or basic medium. The choice of the conditions of deprotection is done judiciously by a person skilled in the art, taking into account the chemical structure of the substrate to be deprotected.

The copolymer prepared according to the process in accordance with the invention can be separated from the reaction medium of step (b) or (c) according to processes well known to those skilled in the art, for example by an operation of evaporation of the solvent under reduced pressure or by a steam stripping operation.

Step (a) of the process in accordance with the invention requires the preparation of the compound of formula (II). The compound of formula (II) is prepared by the copolymerization of a monomer mixture containing the monomer M1 and the monomer M2 in the presence of a catalytic system comprising a transfer agent of formula (III) and a metallocene catalyst,

Y((CH ₂ ) _d B1) _y (III)

Y, B1, d and y being as defined previously, in particular in the various described embodiments of the invention.

The copolymerization of a monomer mixture containing a conjugated diene and a monoolefin such as ethylene, an α-monoolefin or their mixture can be carried out in accordance with patent applications EP1 092 731 , WO 2004035639 , WO2005028526 , WO 2007054223 And WO 2007054224 . knowing that the co-catalyst of the catalytic systems described in these documents is replaced in the present case by the transfer agent. Furthermore, those skilled in the art adapt the polymerization conditions described in these documents so as to achieve the desired microstructure and macrostructure of the copolymer chain A. According to any one of the embodiments of the invention, the molar ratio of the transfer agent to the metal Met constituting the metallocene catalyst is preferably within a range ranging from 1 to 100, more preferably is greater than or equal to 1 and less than 10. The range of values ranging from 1 to less than 10 is in particular more favorable for obtaining copolymers of high molar masses.

Furthermore, a person skilled in the art adapts the polymerization conditions and the concentrations of each of the reagents (constituents of the catalytic system, monomers, stopper), according to the equipment (tools, reactors) used to carry out the polymerization and the various chemical reactions. As is known to those skilled in the art, the copolymerization as well as the handling of the monomers, of the catalytic system and of the polymerization solvent(s) take place under anhydrous conditions and under an inert atmosphere. Polymerization solvents are typically hydrocarbon, aliphatic or aromatic solvents.

The monomer M1 is preferably a monomer chosen from the group consisting of 1,3-butadiene, isoprene and their mixture, more preferably is 1,3-butadiene. The monomer M2 is ethylene or a mixture of ethylene and an α-monoolefin. Suitable α-monoolefins are those mentioned above, namely aliphatic or aromatic α-monoolefins, particularly aliphatic α-monoolefins preferably having 3 to 18 carbon atoms such as propene, 1-butene, 1-hexene, 1-octene, 1-hexadecene or mixtures thereof.

The transfer agent is preferably of formula (III-a) or (III-b), with d ranging from 1 to 11, preferably being equal to 3. The embodiment in which d is equal to 3 is advantageous in particular from the point of view of the accessibility of the transfer agent, since the reagent necessary for its synthesis is a commercial product or a product which is also easily accessible by synthesis.

Mg[(CH ₂ ) _d -N(SiMe ₂ CH ₂ CH ₂ SiMe ₂ )] ₂ (III-a)

Mg[(CH ₂ ) _d -N(SiMe ₃ ) ₂ ] ₂ (III-b)

When Y is an alkaline earth metal or zinc, the transfer agent can be prepared by reaction of the metallic form of Y, called reactive, with a substrate of formula X-(CH ₂ ) _d -B1, B1 and d being as defined previously, X being a halogen, preferably a bromine atom. When Y is Al, the transfer agent of formula (III) is preferably prepared by reaction of AlCl ₃ with a derivative of a compound of formula X-(CH ₂ ) _d -B1 described above, this derivative possibly being an ionic salt based on lithium or potassium, for example of the respective formula Li(CH ₂ ) _d -B1 or K(CH ₂ ) _d -B1 or their form complexed with a solvent, as is well known in organometallic compounds based on lithium or potassium.

The transfer agent is typically synthesized under operating conditions generally used in the synthesis of organometallic compounds, that is to say under anhydrous conditions and under an inert atmosphere, in ether solvents, by a controlled addition of a solution of the substrate, such as a drop by drop, to the reagent in suspension in the solvent. The transfer agent is recovered in a manner known per se, for example by evaporation of the synthesis solvent or by recrystallization from a solvent or a mixture of solvents.

According to a first variant of the process, the metallocene catalyst is a metallocene comprising the unit (in English “moiety”) of formula (IV-1)

P(Cp ¹ )(Cp ² )Met (IV-1)

Met being a group 4 metal atom or a rare earth metal atom,
Cp ¹ and Cp ² , identical or different, being chosen from the group consisting of cyclopentadienyl groups, indenyl groups and fluorenyl groups, the groups possibly being substituted or not,

P being a group bridging the two groups Cp ¹ and Cp ² , and comprising at least one atom silicon or carbon.

In formula (IV-1), the Met atom is connected to a ligand molecule consisting of the two groups Cp ¹ and Cp ² linked together by the bridge P.

According to a second variant of the process, the metallocene catalyst is a metallocene comprising the unit (in English “moiety”) of formula (IV-2)

(Cp ¹ )(Cp ² )Met (IV-2)

Met being a group 4 metal atom or a rare earth metal atom,
Cp ¹ and Cp ² , identical or different, being chosen from the group consisting of cyclopentadienyl groups, indenyl groups and fluorenyl groups, the groups possibly being substituted or not.

It is recalled that the rare earths are metals and designate the elements scandium, yttrium and the lanthanides whose atomic number varies from 57 to 71.

As substituted cyclopentadienyl, fluorenyl and indenyl groups, mention may be made of those substituted by alkyl radicals having 1 to 6 carbon atoms or by aryl radicals having 6 to 12 carbon atoms. The choice of the radicals is also oriented by the accessibility to the corresponding molecules which are the substituted cyclopentadienes, fluorenes and indenes, because the latter are commercially available or easily synthesized.

In the case of a bridged metallocene of formula (IV-1), as substituted cyclopentadienyl group, particular mention may be made of those substituted in position 2 or 3, such as tetramethylcyclopentadienyl or 3-trimethylsilylcyclopentadienyl groups. Position 2 (or 5) designates the position of the carbon atom which is adjacent to the carbon atom to which the P bridge is attached, as shown in the diagram below.

In the case of a bridged metallocene of formula (IV-1), as indenyl group substituted in position 2, particular mention may be made of those substituted in position 2 such as 2-methylindenyl or 2-phenylindenyl groups. Position 2 denotes the position of the carbon atom that is adjacent to the carbon atom to which the P bridge is attached, as shown in the diagram below.

In the case of a bridged metallocene of formula (IV-1), as substituted fluorenyl groups, mention may more particularly be made of the 2,7-ditertiobutyl-fluorenyl and 3,6-ditertiobutyl-fluorenyl groups. Positions 2, 3, 6 and 7 respectively designate the position of the carbon atoms of the cycles as shown in the diagram below, position 9 corresponding to the carbon atom to which the bridge P is attached.

In the case of an unbridged metallocene of formula (IV-2), as substituted cyclopentadienyl group, mention may be made of 3-trimethylsilylcyclopentadienyl, tetramethylcyclopentadienyl; as a substituted indenyl group, mention may be made of methylindenyl and phenylindenyl groups; as substituted fluorenyl groups, mention may be made of the 2,7-ditertiobutyl-fluorenyl and 3,6-ditertiobutyl-fluorenyl groups.

Advantageously, whether the metallocene is of formula (IV-1) or (IV-2), Cp ¹ represents a substituted or unsubstituted cyclopentadienyl group and Cp ² represents a substituted or unsubstituted fluorenyl group. More preferably, Cp ¹ represents an unsubstituted cyclopentadienyl group and Cp ² represents an unsubstituted fluorenyl group.

Preferably, the symbol P, designated by the term bridge, corresponds to the formula MR ¹ R ² , M representing a silicon or carbon atom, preferably a silicon atom, R ¹ and R ² , identical or different, representing an alkyl group comprising from 1 to 20 carbon atoms. More preferably, the bridge P has the formula SiR ¹ R ² , R ¹ and R ² , being as defined previously. Even more preferentially, it corresponds to the formula SiMe ₂ .

Whether the metallocene is of formula (IV-1) or (IV-2), the symbol Met preferably represents a rare earth metal atom, more preferably a lanthanide (Ln) atom whose atomic number ranges from 57 to 71, even more preferably a neodymium (Nd).

• Met représente un atome de métal de terre rare,
• le symbole G désignant un halogène X choisi dans le groupe constitué par le chlore, le fluor, le brome et l'iode, ou un groupe comprenant le motif borohydrure BH₄,
• P, Cp¹ et Cp² étant tels que définis précédemment,
• b étant égal à 1 ou 2.

According to a preferred embodiment of the invention, the metallocene catalyst is of formula (IV-1a) or (IV-2b)

{P(Cp ¹ )(Cp ² )Met-G} _b (IV-1a)

{(Cp ¹ )(Cp ² )Met-G} _b (IV-2b)

in which

• Met represents a rare earth metal atom,
• the symbol G designating a halogen X chosen from the group consisting of chlorine, fluorine, bromine and iodine, or a group comprising the borohydride unit BH ₄ ,
• P, Cp ¹ and Cp ² being as defined previously,
• b being equal to 1 or 2.

Whether the metallocene is of formula (IV-1a) or (IV-2b), the symbol Met preferably represents a lanthanide (Ln) atom whose atomic number ranges from 57 to 71, more preferably a neodymium atom (Nd).

The metallocene can be in the form of crystallized powder or not, or even in the form of monocrystals. The metallocene can be present in a monomer or dimer form, these forms depending on the mode of preparation of the metallocene, as for example that is described in the applications WO 2007054223 And WO 2007054224 . The metallocene can be prepared conventionally by a process analogous to that described in the documents EP 1 092 731 , WO 2007054223 And WO 2007054224 , in particular by reaction under inert and anhydrous conditions of the salt of an alkali metal of the ligand with a rare earth salt such as a halide or a rare earth borohydride, or a salt of a group 4 metal in a suitable solvent, such as an ether, such as diethyl ether or tetrahydrofuran or any other solvent known to those skilled in the art. After reaction, the metallocene is separated from the reaction by-products by techniques known to those skilled in the art, such as filtration or precipitation in a second solvent. The metallocene is finally dried and isolated in solid form.

Advantageously, whether the metallocene is of formula (IV-1a) or (IV-2b), Cp ¹ represents a substituted or unsubstituted cyclopentadienyl group and Cp ² represents a substituted or unsubstituted fluorenyl group. More preferably, Cp ¹ represents an unsubstituted cyclopentadienyl group and Cp ² represents an unsubstituted fluorenyl group. The unsubstituted fluorenyl group has the formula C ₁₃ H ₈ .

According to any one of the embodiments described, the metallocene catalyst is preferably a lanthanide borohydride metallocene or a lanthanide halide metallocene, in particular a lanthanide chloride metallocene.

• L représente un métal alcalin choisi dans le groupe constitué par le lithium, le sodium et le potassium
• N représente une molécule d'un éther,
• x, nombre entier ou non, est égal ou supérieur à 0,
• c, nombre entier, est égal ou supérieur à 0.

According to a particularly preferred embodiment of the invention, the symbol G denotes chlorine or the group of formula (IV)

(BH ₄ ) _(1+c)- L _c -N _x (IV)

in which

• L represents an alkali metal selected from the group consisting of lithium, sodium and potassium
• N represents a molecule of an ether,
• x, whole number or not, is equal to or greater than 0,
• c, whole number, is equal to or greater than 0.

Suitable ether is any ether which has the power to complex the alkali metal, in particular diethyl ether and tetrahydrofuran.

More preferably, the metallocene catalyst is of formula (IV-3a) or (IV-3b) or (IV-3c).

[Me ₂ Si(C ₅ H ₄ )(C ₁₃ H ₈ )NdCl] (IV-3a)

[Me ₂ Si(C ₅ H ₄ )(C ₁₃ H ₈ )Nd(BH ₄ ) ₂ Li(THF)] (IV-3b)

[Me ₂ Si(C ₅ H ₄ )(C ₁₃ H ₈ )Nd(BH ₄ )(THF)] (IV-3c)

• H représentant un atome d'hydrogène ;
• A représentant la chaîne copolymère telle que définie précédemment selon l'un quelconque des modes de réalisation de l'invention ;
• B et d étant tels que définis précédemment selon l'un quelconque des modes de réalisation de l'invention.

Thus, the use of the transfer agent, another object of the invention, makes it possible to access the copolymers in accordance with the invention, whether they are monofunctional at the end of the chain or telechelic. Such copolymers correspond in particular to the following formulas (V) and (VI)

HA-( _CH2 ) _d -B(V)

ZA-( _CH2 ) _d -B(VI)

• H representing a hydrogen atom;
• A representing the copolymer chain as defined previously according to any one of the embodiments of the invention;
• B and d being as defined previously according to any one of the embodiments of the invention.

• y étant égal à 2 ou 3,
• lorsque y = 2, le symbole Y étant un alcalino-terreux ou le zinc, et lorsque y = 3, Y étant l'aluminium ;
• d étant un nombre entier de 0 à 50, avantageusement de 0 à 11 ;
• le symbole A représentant la chaîne copolymère A définie selon l'un quelconque des modes de réalisation décrits,
• B1 étant choisi dans le groupe constitué par N(SiMe₃)₂; N(SiMe₂CH₂CH₂SiMe₂); para-C₆H₄(NMe₂); para-C₆H₄(OMe); para-C₆H₄(N(SiMe₃)₂); ortho-CH₂-C₆H₄NMe₂; ortho-CH₂-C₆H₄OMe; C₆F₅; C₃F₇; C₆F₁₃; CH(OCH₂CH₂O).

A subject described herein is the compound of formula (II), the preparation of which is required in step (a) of the process in accordance with the invention,

Y(A-(CH ₂ ) _d -B1) _y (II)

• y being equal to 2 or 3,
• when y = 2, the symbol Y being an alkaline earth or zinc, and when y = 3, Y being aluminum;
• d being an integer from 0 to 50, advantageously from 0 to 11;
• the symbol A representing the copolymer chain A defined according to any one of the embodiments described,
• B1 being chosen from the group consisting of N(SiMe ₃ ) ₂ ; N(SiMe ₂ CH ₂ CH ₂ SiMe ₂ ); para-C ₆ H ₄ (NMe ₂ ); para-C ₆ H ₄ (OMe); para-C ₆ H ₄ (N(SiMe ₃ ) ₂ ); ortho-CH ₂ -C ₆ H ₄ NMe ₂ ; ortho-CH ₂ -C ₆ H ₄ OMe; _{C6F5 ; C3F7 ; C6F13 ;} CH(OCH ₂ CH ₂ O).

More particularly, the compound of formula (II) is such that Y is Mg, B1 represents the N(SiMe ₂ CH ₂ CH ₂ SiMe ₂ ) group or the N(SiMe ₃ ) ₂ group and d ranges from 1 to 11 or equal to 3.

The copolymer in accordance with the invention, in particular when it is an elastomer, can be used in a rubber composition, in particular in a semi-finished product for a tire.

The rubber composition in accordance with the invention may contain, in addition to the copolymer, any ingredient traditionally used in a rubber composition for tires, such as for example a reinforcing filler such as a carbon black or a silica, a plasticizing system, a crosslinking system, in particular vulcanization, one or more antioxidants.

The aforementioned features of the present invention, as well as others, will be better understood on reading the following description of several embodiments of the invention, given by way of non-limiting illustration.

He. EXAMPLES OF REALIZATION OF THE INVENTION II.1-Characterization methods: Size Exclusion Chromatography (SEC):

The SEC analyzes were carried out at high temperature (HT-SEC) using a Viscotek apparatus (from Malvern Instruments) equipped with 3 columns (PLgel Olexis 300 mm x 7 mm ID from Agilent Technologies) and 3 detectors (refractometer, viscometer and light scattering). 200 µL of a sample solution at a concentration of 5 mg mL ^-1 was eluted in 1,2,4-trichlorobenzene using a flow rate of 1 mL min ^-1 at 150°C. The mobile phase was stabilized with 2,6-di(tert-butyl)-4-methylphenol (200 mg L ^-1 ). OmniSEC software was used for data acquisition and analysis. The number-average molar masses Mn and the polydispersity index Ð were calculated by universal calibration using polystyrene standards.

Nuclear Magnetic Resonance (NMR):

High-resolution NMR spectroscopy was performed on a Bruker DRX 400 spectrometer operating at 400 MHz for the proton and 101 MHz for the carbon-13. The acquisitions were made at 363 K using a 5 mm QNP probe for the ¹ H and a 10 mm PSEX probe for the ¹³ C NMR. The samples were analyzed at a concentration of 5-15% by mass. A mixture of tetrachlorethylene (TCE) and deuterated benzene (C6D6) (2/1 v/v) was used as solvent. The chemical shifts are given in units ppm, relative to tetramethylsilane as an internal reference for 1H NMR and to the methylene signal at 30 ppm of the sequence of ethylene units for ¹³ C.

The microstructure of ethylene/butadiene copolymers is determined by ¹³ C NMR according to the method described in Macromolecules 2001, 34, 6304-6311 .

II.2-Example of preparation of a transfer agent: Example 1 : preparation of the transfer agent MgR ₂ (R= 1-propyl-2,2,5,5-tetramethyl-1-aza-2,5-disilacyclopentane, corresponding to the formula -(CH ₂ ) _3- N(SiMe ₂ CH ₂ CH ₂ SiMe ₂ ))

2.6 g (2 equivalents) of magnesium and then 50 mL of dry THF are introduced into a 100 mL flask under an inert argon atmosphere.

13.3 mL (15 g, 1 equivalent) of 1-(3-bromopropyl)-2,2,5,5-tetramethyl-1-aza-2,5-disilacyclopentane are then added dropwise at room temperature.

The 1-(3-bromopropyl)-2,2,5,5-tetramethyl-1-aza-2,5-disilacyclopentane magnesium solution is then recovered by cannulating this solution into a Schlenk tube under argon in order to remove the unreacted magnesium.

5.5 mL (1.2 equivalent) of dioxane are added to this solution in order to shift the Schlenk equilibrium to form the compound MgR ₂ (R=1-propyl-2,2,5,5-tetramethyl-1-aza-2,5-disilacyclopentane) and to precipitate MgBr ₂ .

This solution is then filtered under argon on Celite in order to recover MgR ₂ in solution in THF. 100 mL of BuzO are added to this solution and the THF is distilled under vacuum at room temperature.

A solution of MgR ₂ in Bu ₂ O is thus obtained.

II.2-Examples of preparation of monofunctional copolymers, involving a step (b) of termination by reaction with a compound containing an acid proton and concomitantly a step (c) of modification of the function: Example 2:

8.5 mL (1.96 mmol) of MgR ₂ (0.23 M in dibutyl ether) prepared according to Example 1 are introduced into a flask containing 200 mL of dry toluene.

The solution is transferred under an argon atmosphere into a 250 mL reactor.

A solution of 31.3 mg of complex [Me ₂ SiFlu ₂ Nd(BH ₄ ) ₂ Li(THF)] (Nd = 49 µmol; Mg/Nd = 40).

The argon is removed under vacuum and the reactor is pressurized to 4 bars using a gaseous mixture of ethylene/1,3-butadiene monomer of constant composition (5 molar % of 1,3-butadiene) at 70°C.

The reactor is degassed after 2 h of polymerization and the temperature is brought back to 20°C. The polymerization medium is poured into a 1M methanol/HCl solution and is stirred for 1 hour.

The precipitated polymer is solubilized in toluene and then is precipitated in a methanol solution in order to be washed in this way. The polymer is finally dried.

23.6 g of copolymer carrying at the end of the copolymer chain the NH ₃ Cl function attached to the chain via the —(CH ₂ ) ₃ — group are recovered.

The number-average molar mass is determined by HT-SEC analysis, 150° C.: M _n =9085 g mol ^-1 , Ð = 2.18.

The proton NMR spectrum (2/1 v/vTCE/CeDe, 400 MHz, 363K) shows the signal characteristic of methylene in the α position of ammonium at δ = 2.68 ppm (broad, -CH ₂ -NH ₃ Cl) and that characteristic of the protons of ammonium at δ = 8.59 ppm (broad, -NH ₃ Cl).

The composition of the copolymer is 95.6% mol of ethylene. 1,3-Butadiene is inserted at 24.7 mol% 1,4-trans, 11.0 mol% 1,2 and 64.3 mol% as rings.

Example 3 :

The same procedure as Example 2 is followed for the synthesis of this copolymer but with a monomer mixture containing 20 mol% of 1,3-butadiene.

7.3 g of copolymer carrying at the end of the copolymer chain the NH ₃ Cl function attached to the chain via the —(CH ₂ ) ₃ — group are recovered.

The number-average molar mass is determined by HT-SEC analysis, 150° C.: M _n =6,800 g mol ^-1 , Ð = 2.07.

The proton NMR spectrum (2/1 v/vTCE/CeDe, 400 MHz, 363K) shows the signal characteristic of methylene in the α position of ammonium at δ = 2.68 ppm (broad, -CH ₂ -NH ₃ CI) and that characteristic of the protons of ammonium at δ = 8.62 ppm (broad, -NH ₃ Cl).

The composition of the copolymer is 80.0 mol% ethylene. 1,3-Butadiene is inserted at 19.0 mol% 1,4-trans, 44.5 mol% 1,2 and 36.5 mol% as rings.

Example 4:

The same procedure as Example 2 is followed for the synthesis of this copolymer, but 2.2 mL (0.51 mmol) of MgR ₂ (0.23 M in dibutyl ether) is introduced for 31.3 mg of complex [Me ₂ SiFlu ₂ Nd(BH ₄ ) ₂ Li(THF)] (Nd=49 μmol; Mg/Nd=10.3) and a mixture of monomer at 20 %mol of 1,3-butadiene.

16.8 g of copolymer carrying at the end of the copolymer chain the NH ₃ Cl function attached to the chain via the —(CH ₂ ) ₃ — group are recovered.

The number-average molar mass is determined by HT-SEC analysis, 150° C.: M _n =25,220 g mol ^-1 , Ð = 2.2.

The proton NMR spectrum (2/1 v/vTCE/C ₆ D ₆ , 400 MHz, 363K) shows the characteristic signal of methylene in the α position of ammonium at δ = 2.68 ppm (broad, -C H ₂ -NH ₃ Cl) and that characteristic of the protons of ammonium at δ = 8.62 ppm (broad, -N H ₃ Cl).

The composition of the copolymer is 80.1% mol of ethylene. The 1,3-butadiene is inserted at 17.5 mol% 1,4- trans, 45.2 mol% 1,2 and 37.3 mol% in the form of rings.

Example 5:

The same procedure as Example 4 is followed for the synthesis of this copolymer, but the polymerization this time lasts 4 hours.

27.6 g of copolymer carrying at the end of the copolymer chain the NH ₃ Cl function attached to the chain via the —(CH ₂ ) ₃ — group are recovered.

The number-average molar mass is determined by HT-SEC analysis, 150° C.: M _n =39,730 g mol ^-1 , Ð = 2.3.

The proton NMR spectrum (2/1 v/v TCE/C ₆ D ₆ , 400 MHz, 363K) makes it possible to observe the methylene in the α position of the ammonium at δ=2.68 ppm (broad, -C H ₂ -NH ₃ Cl).

The composition of the copolymer is 79.3% mol of ethylene. The 1,3-butadiene is inserted at 28.1% mol 1,4- trans, 38.7% mol 1,2 and 33.2% mol in the form of rings.

Example 6:

The same procedure as example 2 is followed for the synthesis of this copolymer but with a monomer mixture containing 30 mol% of 1,3-butadiene.

7.3 g of copolymer carrying at the end of the copolymer chain the NH ₃ Cl function attached to the chain via the —(CH ₂ ) ₃ — group are recovered.

The proton NMR spectrum (2/1 v/vTCE/C ₆ D ₆ , 400 MHz, 363K) shows the characteristic signal of methylene in the α position of ammonium at δ = 2.68 ppm (broad, -C H ₂ -NH ₃ Cl) and that characteristic of the protons of ammonium at δ = 8.59 ppm (broad, -N H ₃ Cl).

The composition of the copolymer is 75.3% mol of ethylene. The 1,3-butadiene is inserted at 25.7% mol 1,4-trans, 44.2% mol 1,2 and 30.1% mol in the form of rings.

Example 7:

1.24 mL (284 μmol) of MgR ₂ (0.23 M in dibutyl ether) prepared according to Example 1 is introduced into a flask containing 200 mL of dry toluene. The solution is transferred under an argon atmosphere into a 250 mL reactor. A solution containing 30.7 mg of complex [Me ₂ Si(C ₅ H ₄ )(C ₁₃ H ₈ )Nd(BH ₄ ) ₂ Li(THF)] (Nd=57 μmol; Mg/Nd=5) is then transferred. The argon is removed under vacuum and the reactor is pressurized to 4 bars by means of a gaseous mixture of ethylene/1,3-butadiene monomer of constant composition (20 molar % of 1,3-butadiene) at 80°C. The reactor is degassed after 90 minutes of polymerization and the temperature is brought back to 20°C. The polymerization medium is poured into a 1M methanol/HCl solution and is stirred for 1 hour. The precipitated polymer is re-solubilized in toluene, then is precipitated in a methanol solution to be washed in this way. The polymer is finally dried.

9.89 g of copolymer carrying at the end of the chain a —NH ₃ Cl function (or in the —NH ₂ form) attached to the chain via the —(CH ₂ ) ₃ — group are recovered. The proton NMR spectrum (2/1 v/v TCE/C ₆ D ₆ , 400 MHz, 363K) shows the characteristic signal of methylene in the α position of the amine at δ = 2.53 ppm (broad, -C H ₂ -NH ₂ ) and that of methylene in the α position of the ammonium at δ = 2.68 ppm (broad, -C H ₂ -NH ₃ Cl). The composition of the copolymer is 67.6% mol of ethylene and 32.4% of butadiene. The 1,3-butadiene is inserted in two forms, 97.4 mol% 1,4-trans units and 2.6 mol% 1,2 units.

II.3-Examples of preparation of monofunctional copolymers, involving a step (c) of modification of the function: Example 8, step (c) being a hydrolysis reaction in a basic medium :

A fraction of the polymer of Example 2 is taken (10 g). The polymer is dissolved in toluene and then precipitated using a methanol/NaOH (1M) solution and stirred for 1 hour at room temperature.

The polymer is recovered and then washed with methanol and dried under vacuum at 60°C.

8.2 g of copolymer carrying at the end of the copolymer chain the NH ₂ function attached to the chain via the —(CH ₂ ) ₃ — group are recovered.

The proton NMR spectrum (2/1 v/v TCE/C ₆ D ₆ , 400 MHz, 363K) shows the disappearance of the characteristic signals of ammonium at δ = 2.68 ppm, (broad, -C H ₂ -NH ₃ Cl) and δ = 8.59 ppm, (broad, -N H ₃ Cl) in favor of the characteristic signal of methylene in the α position of the amine at δ = 2.5 3 ppm (broad, -CH 2 _{-NH 2} ).

Example 9, step (c) being a hydrolysis reaction in a basic medium :

A fraction of the polymer of Example 3 is taken (8 g). The polymer is dissolved in toluene and then precipitated using a methanol/NaOH (1M) solution and stirred for 1 hour at room temperature.

The polymer is recovered and then washed with methanol and dried under vacuum at 60°C.

7.8 g of copolymer carrying at the end of the copolymer chain the NH ₂ function attached to the chain via the —(CH ₂ ) ₃ — group are recovered.

The proton NMR spectrum (2/1 v/v TCE/C ₆ D ₆ , 400 MHz, 363K) shows the disappearance of the characteristic signals of ammonium at δ = 2.68 ppm, (broad, -C H ₂ -NH ₃ Cl) and δ = 8.62 ppm, (broad, -N H ₃ Cl) in favor of the characteristic signal of methylene in the α position of the amine at δ = 2.5 3 ppm (broad, -CH 2 _{-NH 2} ).

Example 10, step (c) being a hydrolysis reaction in a basic medium :

A fraction of the polymer of Example 4 is taken (7 g). The polymer is dissolved in toluene and then precipitated using a methanol/NaOH (1M) solution and stirred for 1 hour at room temperature.

The polymer is recovered and then washed with methanol and dried under vacuum at 60°C.

5.3 g of copolymer carrying at the end of the copolymer chain the function NH ₂ attached to the chain through the -(CH ₂ ) ₃ - group.

Example 11, step (c) being a hydrolysis reaction in a basic medium :

A fraction of the polymer of Example 5 is taken (13 g). The polymer is dissolved in toluene and then precipitated using a methanol/NaOH (1M) solution and stirred for 1 hour at room temperature.

The polymer is recovered and then washed with methanol and dried under vacuum at 60°C.

12.0 g of copolymer carrying at the end of the copolymer chain the NH ₂ function attached to the chain via the —(CH ₂ ) ₃ — group are recovered.

The proton NMR spectrum (2/1 v/v TCE/C ₆ D ₆ , 400 MHz, 363K) shows the disappearance of the characteristic signal of ammonium observed at δ = 2.68 ppm, (broad, -C H ₂ -NH ₃ Cl) in favor of the characteristic signal of methylene in the α position of the amine at δ = 2.53 ppm (broad, -C H ₂ -NH ₂ ).

Example 12, step (c) being a hydrolysis reaction in a basic medium:

A fraction of the polymer of Example 6 is taken (3 g). The polymer is dissolved in toluene and then precipitated using a methanol/NaOH (1M) solution and stirred for 1 hour at room temperature.

The polymer is recovered and then washed with methanol and dried under vacuum at 60°C.

2.5 g of copolymer carrying at the end of the copolymer chain the NH ₂ function attached to the chain via the —(CH ₂ ) ₃ — group are recovered.

The proton NMR spectrum (2/1 v/v TCE/C ₆ D ₆ , 400 MHz, 363K) shows the disappearance of the characteristic signals of ammonium at δ = 2.68 ppm, (broad, -C H ₂ -NH ₃ Cl) and δ = 8.59 ppm, (broad, -N H ₃ Cl) in favor of the characteristic signal of methylene in the α position of the amine at δ = 2.5 3 ppm (broad, -CH 2 _{-NH 2} ).

II.4-Example of preparation of a telechelic copolymer, involving a step (b) of termination by reaction with a functionalizing agent: Example 13: Preparation of a telechelic EBR Z-EBR-(CH ₂ ) ₃ -B (with Z = I; B = NH ₃ Cl) with a feed containing 20% mol of 1,3-butadiene

8.5 mL (1.96 mmol) of MgR ₂ (0.23 M in dibutyl ether) prepared according to Example 1 are introduced into a flask containing 200 mL of dry toluene.

The solution is transferred under an argon atmosphere into a 250 mL reactor.

A solution of 31.3 mg of complex [Me ₂ SiFlu ₂ Nd(BH ₄ ) ₂ Li(THF)] (Nd=49 μmol; Mg/Nd=40) is then transferred.

The argon is removed under vacuum and the reactor is pressurized to 4 bars by means of a gaseous mixture of ethylene/1,3-butadiene monomer of constant composition (20% molar of 1,3-butadiene) at 70°C.

The reactor is degassed after 2 h of polymerization and the temperature of the medium reaction is maintained at 70°C.

In order to have a reference copolymer before the reaction with the functionalizing agent, in this case the monofunctional copolymer, a sample of 100 mL of the reaction medium is then taken. This sample is poured into a 1M methanol/HCl solution and is stirred for 1 hour. The precipitated reference polymer is solubilized in toluene and then is precipitated in a methanol solution in order to be washed in this way.

The polymer is finally dried.

7.4 g of copolymer carrying at the end of the copolymer chain the NH ₃ Cl function attached to the chain via the —(CH ₂ ) ₃ — group are recovered.

The proton NMR spectrum (2/1 v/v TCE/C ₆ D ₆ , 400 MHz, 363K) shows the signal characteristic of methylene in the α position of ammonium at δ = 2.68 ppm (broad, -C H ₂ -NH ₃ Cl) and that characteristic of the protons of ammonium at δ = 8.58 ppm (broad, -N H ₃ Cl)
The composition of the reference copolymer is 80.8% mol of ethylene. The 1,3-butadiene is inserted at 18.7% mol 1,4- trans, 39.9% mol 1,2 and 41.4% mol in the form of rings.

To the reaction medium, a solution of 3.8 g of iodine (15 mmol) in THF (1/Mg molar ratio=15) is added and the mixture is stirred for 2 hours at 70°C.

The temperature is brought back to 20°C. The polymerization medium is poured into a 1M methanol/HCl solution and is stirred for 1 hour.

The precipitated polymer is solubilized in toluene and then is precipitated in a methanol solution in order to be washed in this way.

The polymer is finally dried.

6.3 g of copolymer are recovered bearing at one chain end the NH ₃ Cl function attached to the chain via the —(CH ₂ ) ₃ — group and at the other chain end the I function.

The proton NMR spectrum (2/1 v/vTCE/C ₆ D ₆ , 400 MHz, 363K) shows the characteristic signal of methylene in the α position of ammonium at δ = 2.68 ppm (broad, -C H ₂ -NH ₃ Cl) and that characteristic of the protons of ammonium at δ = 8.52 ppm (broad, -N H ₃ Cl) but also that characteristic of methylenes in the α position of an iodo group at δ=2.94 ppm (multiplet, -C H ₂ -I).

Claims (14)

1. Copolymer comprising a copolymer chain A bearing a function B selected from the group consisting of the functions B1 and B2,

   • the copolymer chain A being a copolymer chain comprising monomer units M1 and monomer units M2, M1 being a conjugated diene,

   • B1 being selected from the group consisting of N(SiMe₃)₂; N(SiMe₂CH₂CH₂SiMe₂); para-C₆H₄(NMe₂); para-C₆H₄(OMe); para-C₆H₄(N(SiMe₃)₂); ortho-CH₂-C₆H₄NMe₂; ortho-CH₂-C₆H₄OMe; C₆F₅; C₃F₇; C₆F₁₃; CH(OCH₂CH₂O);

   • B2 being a function that is derived from B1;

   the function B being borne at the end of the copolymer chain A;

   M2 being ethylene or a mixture of ethylene and an α-monoolefin.
2. Copolymer according to Claim 1, wherein the function B is attached to the copolymer chain A directly by a covalent bond or via a divalent group of formula (I)
   
           -(CH₂)_w-     (I)
   
   wherein w is an integer from 1 to 50, preferably w varies in a range extending from 1 to 11, more preferably is equal to 3.
3. Copolymer according to any one of Claims 1 to 2, wherein the function B1 is the N(SiMe₂CH₂CH₂SiMe₂) group or the N(SiMe₃)₂ group.
4. Copolymer according to any one of Claims 1 to 3, wherein the function B2 is selected from the group consisting of amines, ammoniums and ketones.
5. Copolymer according to any one of Claims 1 to 4, wherein the function B2 is an amine, preferably a primary amine.
6. Copolymer according to any one of Claims 1 to 5, wherein the ethylene units represent more than 50 mol%, preferentially more than 65 mol% of the monomer units of the copolymer.
7. Copolymer according to any one of Claims 1 to 6, wherein the monomer units M1 contain more than 80 mol% of a moiety resulting from a trans-1,4 insertion of M1 into the copolymer chain.
8. Process for preparing a copolymer comprising a copolymer chain A according to claim 1, which process comprises step (a), step (b) and where appropriate step (c) below:

   • (a) preparation of a compound of formula (II)
   
           Y(A-(CH₂)_d-B1)_y     (II)
   
   wherein

   o y is equal to 2 or 3;

   o when y = 2, the symbol Y is an alkaline-earth metal or zinc, and when y = 3, Y is aluminium;

   o d is an integer from 0 to 50, advantageously from 0 to 11;

   o the symbol A representing a copolymer chain A comprising monomer units M1 and monomer units M2, M1 being a conjugated diene;

   o B1 is selected from the group consisting of N(SiMe₃)₂; N(SiMe₂CH₂CH₂SiMe₂); para-C₆H₄(NMe₂); para-C₆H₄(OMe); para-C₆H₄(N(SiMe₃)₂); ortho-CH₂-C₆H₄NMe₂; ortho-CH₂-C₆H₄OMe; C₆F₅; C₃F₇; C₆F₁₃; CH(OCH₂CH₂O),

   • (b) a reaction for terminating the copolymer chain A,

   • (c) a reaction for modifying the function B1 into the function B2 defined according to claim 1, M2 being ethylene or a mixture of ethylene and an α-monoolefin,

   the compound of formula (II) being prepared by the copolymerization of a monomer mixture containing the monomer M1 and the monomer M2 in the presence of a catalytic system comprising a transfer agent of formula (III) and a metallocene catalyst comprising the moiety of formula (IV-1) or (IV-2)
   
           Y((CH₂)_dB1)_y     (III)
   
           P(Cp¹)(Cp²)Met     (IV-1)
   
           (Cp¹)(Cp²)Met     (IV-2)
   
   

   Met being a group 4 metal atom or a rare-earth metal atom,

   P being a group that bridges the two Cp¹ and Cp² groups, and that comprises at least one silicon or carbon atom,

   Cp¹ and Cp², which are identical or different, being selected from the group consisting of cyclopentadienyl groups, indenyl groups and fluorenyl groups, it being possible for the groups to be substituted or unsubstituted.
9. Process according to Claim 8, wherein the transfer agent is of formula (III-a) or (III-b), with d ranging from 1 to 11:
   
           Mg[(CH₂)_d-N(SiMe₂CH₂CH₂SiMe₂)]₂     (III-a)
   
           Mg[(CH₂)_d-N(SiMe₃)₂]₂     (III-b)
   
   
10. Process according to Claim 9, wherein d is equal to 3.
11. Process according to any one of Claims 8 to 10, wherein Met represents a rare-earth metal atom, preferably a lanthanide atom Ln, the atomic number of which ranges from 57 to 71, more preferentially a neodymium atom.
12. Process according to any one of Claims 8 to 11, wherein the metallocene catalyst is of formula (IV-1a) or (IV-2b):
    
            {P(Cp¹)(Cp²)Met-G}_b     (IV-1a)
    
            {(Cp¹)(Cp²)Met-G}_b     (IV-2b)
    
    

    - the symbol G denoting a halogen X selected from the group consisting of chlorine, fluorine, bromine and iodine or a group comprising the BH₄ borohydride moiety,

    - P, Cp¹ and Cp² being as defined in Claim 8,

    - Met being as defined in Claim 11,

    - b being equal to 1 or 2.
13. Compound of formula (II) as defined in Claim 8, preferably with Y being Mg, B1 representing the N(SiMe₂CH₂CH₂SiMe₂) group or the N(SiMe₃)₂ group and d ranging from 1 to 11 or being equal to 3.
14. Rubber composition that comprises a copolymer defined according to any one of Claims 1 to 7, the copolymer being an elastomer.